Servo-control apparatus for motor

ABSTRACT

A servo-control apparatus for a motor includes a position detector for detecting a rotational position of a motor, a rotational speed signal generator for generating a rotational speed signal corresponding to a rotational speed of a motor, and a digital controller for generating an exciting electric current to be supplied to a coil of the motor as a pulse width modulated signal in accordance with the rotational speed signal from the rotational speed signal generator. A switching signal for switching the exciting electric current to be supplied to the coil of the motor is formed by a pre-driver in accordance with the position detection signal from the position detector, and the pre-driver combines the switching signal with the pulse width modulated signal from the digital controller to generate an electric current control signal by which the motor is driven, thereby coping with the speed change of the motor quickly and stably.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a servo-control apparatus for motor,servo-controlling a motor by using a DSP as digital control means, andmore particularly it relates to a motor servo-control apparatus suitablefor controlling a plurality of motors used in an image formingapparatus.

2. Related Background Art

FIGS. 12 and 13 are conventional circuit diagrams for effectingservo-control of a plurality of motors by using a micro computer.Particularly, FIG. 12 is a block diagram showing an entire circuit inwhich a plurality of motor units 301 having the same construction areconnected to a single micro computer 300, and FIG. 13 is a block diagramshowing an internal construction of one of the motor units 301.

Now, the conventional servo-control will be described. In FIGS. 12 and13, there are shown a micro computer 300, motor units 301, a control IC302, a three-phase motor 303, three hole sensors 304 for detecting aposition of a main pole of a rotor, an FG sensor 305 for detecting apattern magnetized on the rotor and for outputting 36 pulses per onerevolution of the motor, an oscillator 306, a current detecting resistor307, a control portion 308, a driver portion 309, an electric currentlimiter detecting portion 310, a speed control portion 311, a frequencydivider 312, an integration amplifier 313, resistors and capacitorsconstituting integration filters 314 to 317, a control signal 318emitted from the micro computer 300 and adapted to drive/stop the motor,and a ready signal 319 which becomes active when the motor reaches apredetermined revolution number.

Next, an operation of the circuit will be described. When a motordriving command is emitted from the micro computer 300 controlling animage forming apparatus through the signal line 318, the control portion308 detects the position of the main pole of the rotor of the motor 303by the hole sensors 304 and forms a three-phase exciting pattern so asto rotate the motor in a desired direction and sends an exciting signalto the driver portion 309. On the basis of the exciting signal, thedriver portion 309 drives an output transistor (not shown) so that anelectric current direction with respect to a coil of the motor isswitched to generate desired excitation. On the other hand, when therotor of the motor 303 is rotated, predetermined pulses are generated bythe FG sensor 305 and are sent to the speed control portion 311. In thespeed control portion 311, a reference clock formed by the oscillator306 and the frequency divider 312 is compared with the pulse detected bythe FG sensor 305, and the difference therebetween is outputted.

Incidentally, the reference clock is set to obtain a target revolutionnumber (number of revolutions) of the motor. Namely, when the FG sensoroutputs 30 pulses per one revolution of the motor, in order to rotatethe motor at 600 rpm, the reference clock of 300 Hz (=(600/60)×30) maybe given.

The difference with respect to the target speed obtained by the speedcontrol portion 311 is integrated by the integration amplifier 313, anda result is sent to the driver portion 309. In this case, gain and aphase compensation value are determined by the resistors and capacitors314 to 317. These constants are referred to as servo constants.

Further, in the driver portion 309 for the motor of the conventionalimage forming apparatus, a transistor of bipolar type is used. Thus,since heat loss of the driver portion is great, a radiator plate isprovided. Further, in order to reduce heat generation due to such heatloss as much as possible, the efficiency of the motor must be increasedso that the desired power can be obtained with the least electric power.To this end, a brushless motor of the outer rotor type having goodefficiency is used.

As mentioned above, in the conventional circuit arrangement, the motoris controlled by sending only stop/start signals to the motor units 301from the micro computer 300, and a servo-control loop is formed in eachmotor unit 301. The reason for this is that, since the processingability of the conventional micro computer is limited, servo-controlmust be effected in each motor unit 301. As the processing ability ofthe micro computer or a DSP (digital signal processor) has beenimproved, servo-control for the motors has been able to be effected bythe micro computer or the DSP itself. Further, due to an increase inprocessing ability of the DSP, a plurality of motors have been able tobe servo-controlled independently.

As a result, in place of the above-mentioned conventional circuitarrangement, it has been considered to provide a circuit having motorsservo-controlled by the DSP. Such a circuit will be explained hereinbelow. FIGS. 14 and 15 are views showing such a circuit. Particularly,FIG. 14 is a block diagram showing an entire circuit in which aplurality of motor units are connected to a single DSP, and FIG. 15 is ablock diagram showing the internal construction of one of the motorunits.

In FIGS. 14 and 15, there are shown a DSP 501 serving to control sixmotors 505, motor units 502 each including a drive circuit, a driver504, a three-phase DC brushless motor 505, a charge pump circuit 401 forgenerating gate voltage for N-chMOS of the driver 504, pre-drivercircuits 402 to 407, exciting switching signals 408 to 413, a currentsense signal 414, hole sensor signals 415 to 417, an MR sensor signal418, hole sensor amplifiers 419 to 421, an MR sensor amplifier 422,N-chMOS transistors (driver portions) 515 to 520, a current detectingresistor 521, U-phase output 522 connected to a U-phase coil of themotor, V-phase output 523 connected to a V-shape coil, W-phase output524 connected to a W-phase coil, hole sensors 525 to 527, an MR sensor528, and a serial communication bus 532 for effecting communication witha control CPU (not shown) of the image forming apparatus.

Next, an operation of this servo-control circuit will be described.First of all, when a motor drive command is transmitted from the CPUthrough the serial communication line 532, the DSP 501 ascertains theposition of the rotor detected by the hole sensors 525 to 527 on thebasis of the hole sensor signals 415 to 417 and determines the switchingtiming so as to obtain the desired rotation and effects control on thebasis of the switching signals 408 to 413 to give a desired rotationaldirection and a desired electric current to the motor.

Namely, the N-chMOS transistors 515 to 520 are switched to give thedesired rotational direction, and the N-chMOS transistors 515, 517, 519are PWM-switched to cause the desired electric current to flow into thecoil of the motor. In this case, the gate voltages of the N-chMOStransistors 515, 517, 519 are increased to Vcc+10V by the charge pumpcircuit 401.

For example, when the DSP 501 ascertains the rotor position of the motoron the basis of the hole sensor signals 415 to 417 amplified by the holesensor amplifiers 419 to 421 and the hole sensors 525 to 527 andswitches the direction of the electric current from the U-phase 522 tothe W-phase 523 to obtain the desired rotational direction, thepre-drivers 402 to 407 turn ON the N-chMOS transistors 515, 518 and turnOFF the transistors 516, 517, 519, 520. As a result, an electric currentpath extends from Vcc to the current detecting resistor 521 through thetransistor 515, U-phase output 522, V-phase output 523 and transistor518, thereby generating a magnetic force in the desired coil. In thiscase, the PWM signal given by the DSP 501 is composed or combined withthe switching signal 408, so that the N-chMOS transistor 515 isPWM-controlled by the pre-driver 402.

Accordingly, ON-duty electric current defined by the PWM signal flowsfrom the U-phase to the V-phase. In this way, the motor is subjected toexciting switching control for switching the electric current to U, V,W-phase to rotate the rotor in the desired rotational direction, therebygenerating torque by relative electromagnetic action between the mainpole magnet (not shown) and the coil.

When the motor is subjected to the exciting switching control in thisway to rotate the rotor, a pre-set MR sensor magnetizing pattern isdetected by the MR sensor 528, thereby outputting 360 pulses per onerevolution. Namely, a signal having frequency corresponding to therevolution number of the motor is obtained, and this signal is inputtedto the DSP 501 as the MR sensor signal 418 through the amplifier 422.

The DSP 501 measures a pulse interval of the MR sensor signal 418 andseeks the speed (rad/s) of the motor and compares the motor speed with atarget control speed and performs PI filter (not shown) and gain addedcalculation (not shown) to derive PWM pulse width and combines the pulsewidth with the switching signals 408, 410, 412 to control the current tobe supplied to the motor coil, thereby controlling the motor to rotateat the target speed.

In this way, the DSP 501 effects the switching of the output stageN-chMOS transistor by generating the PWM signal and combining it withthe switching signals, thereby performing the servo-control to rotatethe motor at the desired number of revolutions. On the other hand, theposition of the main pole is detected by the hole sensors 525 to 527,and the switching control is performed on the basis of the hole sensorsignals 415 to 417 to rotate the rotor in the desired rotationaldirection. Further, the current flowing through the motor is detected bythe electric current detecting resistor 521, and, there is providedprotecting means for limiting the electric current if the currentgreater than a predetermined value flows.

In the conventional motor servo-control apparatus explained inconnection with FIGS. 12 and 13, the micro computer effects drive/stopcontrol of the drive motors, and each drive motor has serve-control ICand the serve-control is effected in each motor unit. Namely, thefeedback loop is closed in the motor unit. Further, stability of theservo-control of each motor is determined by constants, i.e., serveconstants of the resistors and capacitors connected to the integrationamplifier of the circuit. Namely, these servo constants were required tobe set so that the motors be rotated most stably and accurately underevery conditions in consideration of load inertia and load torque.

As a result, when the above-mentioned conventional motor servo-controlapparatuses are used as various drive means of an image formingapparatus of electrophotographic type having a cartridge integrallyincluding toner and a photosensitive drum, if the load inertia and thetorque of the drive motor for driving the photosensitive drum is greatlychanged in dependence upon a difference in toner capacity, a differencein the kind of toner, or a difference in the cartridge used, there arosea problem that stable servo-control could not achieved under allconditions.

Further, in a color image forming apparatus, in order to enhance aglossy property of the apparatus, there is provided a glossy print modein which a recording paper is conveyed at a speed slower than a normalrecording paper conveying speed so that a time period during which therecording paper is passed through a fixing device is increased toimprove toner fusion. Thus, the drive motors must be controlled withplural speeds, and, if the speed control range is wide, stableservo-control cannot be obtained by only one servo constant system.

As one method for solving this problem, there has been proposed atechnique in which a plurality of integration amplifiers are providedand the amplifiers are switched in accordance with conditions. However,this technique has a disadvantage that the cost is increasedconsiderably.

Further, in general, speed detecting means for the servo motor isprovided on the motor itself, for the purpose of improvement inrotational accuracy and stability of the rotor of the motor.

In an image forming apparatus using such a motor, for example, iffluctuation in rotation due to fluctuation in load is caused on a shaftof a photosensitive drum, when such fluctuation in rotation can becorrected by the servo-control of the motor, the fluctuation in rotationof the drum shaft can be reduced, thereby obtaining good image quality.However, since the conventional motor is a DC bruchless motor of outerrotor type having a main pole magnet of the rotating rotor, inertia ofthe rotor is great. Accordingly, the fluctuation in rotation generatedon the drum shaft is hard to be transmitted to a drive shaft of the drumdrive motor. As a result, even if the servo-control of the drum drivemotor is performed accurately, unevenness in rotation of the drum cannotbe improved, with the result that deterioration of image quality cannotbe reduced.

Further, there is an image forming apparatus using a stepping motor inplace of the DC brushless motor. However, the stepping motor has lowefficiency in comparison with the DC brushless motor. Thus, particularlyin the color image forming apparatus having a plurality of motors, ifall of the motors are stepping motors, the load on the power supply ofthe apparatus becomes great, thereby increasing the total cost of theapparatus considerably. Further, since the stepping motor generatesgreat vibration during step driving, when the plurality of steppingmotors are used, the noise generated by the apparatus becomes great.

As an apparatus normally considered to eliminate the above-mentioneddisadvantages of the conventional motor servo-control device shown inFIGS. 12 and 13, there is the motor servo-control apparatus explained inconnection with FIGS. 14 and 15. In this servo-control apparatus, sincethe DSP performs all of the phase switching control, speed control, andelectric current limiting control, if the number of the motor unitsconnected to the DSP is increased, adequate processing cannot beachieved. Further, since a great number of signal lines are requiredbetween the DSP and the motor units (for example, eleven signal linesfor each motor unit), the number of input/output pins is increased, withthe result that the control ability of the interfaces may deteriorate.Further, in the electric current limitation, when the electric currentdetection voltage is sent from the motor unit to the DSP, if a distancebetween the motor unit and the DSP is long, noise will be generated.

When digital servo-control of the plural motors is effected by the DSP,if control timings for the motors overlap for the number of motors to becontrolled, since the servo-control period of the motor does not becomeconstant, unevenness in rotation of the motor will occur.

Further, the servo constant of the motor to be servo-controlled isdetermined by the torque constant, the inertia, and the coil resistanceof the motor to be connected.

In such a construction, particularly when motors are purchased fromdifferent companies, the servo constant must be set so that stableservo-control can be achieved under all conditions of torque constants,inertia, and coil resistances of the motors to be used.

For example, the inertia of a motor of the outer-rotor type differsgreatly from the inertia of a motor of the inner-rotor type. In suchmotors having different inertia, the setting of a proper servo constantis limited.

Namely, if the servo constant is set to match the motor of the outerrotor type to enhance the servo stability of the motor of theouter-rotor type, when the motor of the inner-rotor type is used, servostability of such a motor will be worsened.

Thus, in the past, when the servo constant was selected, it wasdifficult to enhance the stability of servo-control of all of the motorsto be used.

SUMMARY OF THE INVENTION

The present invention aims to eliminate the above-mentioned conventionaldrawbacks and an object of the present invention is to provide a motorservo-control apparatus which has a construction suitable for effectingservo-control by using a DSP as digital control means.

Another object of the present invention is to provide a motorservo-control apparatus in which a plurality of motors used in an imageforming apparatus are controlled collectively by using a DSP as digitalcontrol means.

The other objects and features of the present invention will be apparentfrom the following detailed explanation referring to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an image forming apparatus accordingto the present invention;

FIG. 2 is a view showing a motor servo-control apparatus used in theimage forming apparatus of FIG. 1 and particularly showing a blockdiagram of an entire circuit in which a plurality of circuit units areconnected to a single DSP;

FIG. 3 is a block circuit diagram showing the internal circuitry of oneof the plural motor units shown in FIG. 2;

FIG. 4 is a block diagram showing the DSP of FIGS. 1 and 2 concretely;

FIG. 5 is a view showing control of the plural motors of FIG. 4 in atime-lapse relation;

FIG. 6, which is comprised of FIGS. 6A and 6B, is a flow chart showing amotor control program of the DSP including servo-constant calculationcontrol;

FIG. 7A is a view showing a brushless motor of the outer-rotor type as areference, and FIG. 7B is a view showing a brushless motor of theinner-rotor type used in the present invention;

FIG. 8 is a block circuit diagram showing a first alteration of theinternal circuitry of the motor unit shown in FIG. 3;

FIG. 9 is a flow chart of the DSP shown in FIG. 8;

FIG. 10 is a block circuit diagram showing a second alteration of theinternal circuitry of the motor unit shown in FIG. 3;

FIG. 11 is a flow chart of the DSP shown in FIG. 10;

FIG. 12 is a block diagram of an entire circuit showing a conventionalmotor servo-control apparatus in which a plurality of motor units areconnected to a single micro computer;

FIG. 13 is a block circuit diagram showing internal circuitry of one ofthe plural motor units shown in FIG. 12;

FIG. 14 is a block diagram of an entire circuit in which a plurality ofmotor units are connected to a single DSP, which can be considered inconnection with the conventional motor servo-control apparatus; and

FIG. 15 is a block circuit diagram showing internal circuitry of one ofthe plural motor units shown in FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be explained with reference to theaccompanying drawings.

Prior to explanation of a motor servo-control apparatus of the presentinvention, first of all, an image forming apparatus to which the motorservo-control apparatus of the present invention can be applied will bedescribed.

FIG. 1 is a schematic view showing such an image forming apparatus. InFIG. 1, the image forming apparatus 201 comprises a sheet cassette 202,a pick-up roller 203, an electrostatic belt drive roller 204, anelectrostatic belt 205, an yellow photosensitive drum 206, a magentaphotosensitive drum 207, a cyan photosensitive drum 208, a blackphotosensitive drum 209, an yellow transfer roller 210, a magentatransfer roller 211, a cyan transfer roller 212, a black transfer roller213, an yellow cartridge 214, a magenta cartridge 215, a cyan cartridge216, a black cartridge 217, an yellow optical unit 218, a magentaoptical unit 219, a cyan optical unit 220, a black optical unit 221, afixing roller 222 and a sheet path 223.

The image forming apparatus serves to perform an electrophotographicprocess on the basis of a command from a host computer (not shown) totransfer yellow, magenta, cyan and black images onto a paper in asuperimposed fashion. Further, the pick-up roller 203 is driven by apick-up roller motor, the electrostatic belt is driven by a belt motor,the photosensitive drums are driven by respective color drum motors, andthe fixing roller is driven by a fixing motor, and drive/stop of eachmotor is controlled by a servo control apparatus provided in the imageforming apparatus.

FIGS. 2 and 3 are views showing the motor servo-control apparatusaccording to the present invention. Particularly, FIG. 2 is a blockdiagram showing an entire circuit in which six motor units of the imageforming apparatus are connected to a single DSP, and FIG. 3 is a blockdiagram showing an internal construction of one of the motor units(motor unit 502 having an yellow photosensitive drum motor 505 ₁.

FIGS. 2 and 3, a DSP (digital signal processor) 501 as a digital controldevice is capable of performing product/addition calculation quickly.Motor units 502 include drive circuits (pre-driver, driver) and have thesame construction and comprise, from the above, a motor unit having anyellow photosensitive drum motor 505 ₁, a motor unit having a magentaphotosensitive drum motor 505 ₂, a motor unit having a cyanphotosensitive drum motor 505 ₃, a motor unit having a blackphotosensitive drum motor 505 ₄, a motor unit having a belt motor 505 ₅,and a motor unit having a fixing motor 505 ₆. Incidentally, the pick-uproller 203 is driven by a stepping motor, which does not relate to theservo-control apparatus of the present invention. The DSP 501 serves tocontrol six motors 505 ₁ to 505 ₆. As each of these motors, a DCbrushless motor of the inner-rotor type, having a small inertia andcapable of improving control accuracy, is used. In FIG. 3, there areshown a pre-driver 503 having a logic circuit and a control circuitwhich will be described later, a driver 504, a three-phase DC brushlessmotor 505, a regulator 506, a charge pump circuit 507 for generatinggate voltage for N-chMOS of the driver 504, a logic circuit 508 forcomposing or combining a PWM signal from the DSP 501 with switchingsignals (which will be described later), a control circuit 509 forboosting the output from the logic circuit, an electric current limiter510, hole sensor amplifiers 511 to 513, an MR sensor amplifier 514,N-chMOS transistors 515 to 520 provided in the driver, an electriccurrent detecting resistor 521, a U-phase output 522 connected to aU-phase coil of the motor, a V-phase output 523 connected to a V-phasecoil, a W-phase output 524 connected to a W-phase coil, hole sensors 525to 527, an MR sensor 528, a motor start signal (stop/start signal) 529outputted from the DSP, a PWM signal 530 outputted from the DSP, and amotor speed detecting MR sensor signal 531. The logic circuit serves tocombine the switching signals from the hole sensors 525 to 527 throughthe hole sensor amplifiers 511 to 513 with the PWM signal from the DSP501, and the control circuit 509 serves to boost an output signal fromthe logic circuit 508 to be outputted to the driver 504 as an electriccurrent control signal. There is also provided a serial communicationbus 532 for effecting communication with a control CPU (not shown) ofthe image forming apparatus.

Next, an operation of the motor servo-control circuit will be described.First of all, when a motor drive command is transmitted from the CPUthrough the serial communication line 532, the pre-driver 503 ascertainsthe position of the rotor detected by the hole sensors 525 to 527 anddetermines the switching timing so as to obtain the desired rotation andeffects control to give the desired rotational direction and the desiredelectric current to the motor. Namely, the N-chMOS transistors 515 to520 are switched to give the desired rotational direction, and theN-chMOS transistors 515, 517, 519 are PWM-switched to cause the desiredelectric current to flow into the coil of the motor. In this case, thegate voltages of the N-chMOS transistors 515, 517, 519 are increased toVcc+10V by the charge pump circuit 507.

For example, when the pre-driver 503 ascertains the rotor position ofthe motor on the basis of the hole sensor signals amplified by the holesensor amplifiers 511 to 513 and the hole sensors 525 to 527 andswitches the direction of the electric current from the U-phase 522 tothe W-phase 523 to obtain the desired rotational direction, thepre-driver 503 turns ON the N-chMOS transistors 515, 518 and turns OFFthe transistors 516, 517, 519, 520. As a result, an electric currentpath extends from Vcc to the current detecting resistor 521 through thetransistor 515, U-phase output 522, V-phase output 523 and transistor518, thereby generating a magnetic force in the desired coil. In thiscase, the PWM signal 530 given by the DSP 501 is composed or combinedwith the switching signal, so that the N-chMOS transistor 515 isPWM-controlled b the pre-driver 503.

Accordingly, ON-duty electric current defined by the PWM signal flowsfrom the U-phase to the V-phase. In this way, the motor is subjected toexciting switching control for switching the electric current to the U,V, W-phase to rotate the rotor in the desired rotational direction,thereby generating torque by the relative electromagnetic action betweenthe main pole magnet (not shown) and the coil.

When the motor is subjected to the exciting switching control in thisway to rotate the rotor, a pre-set MR sensor magnetizing pattern isdetected by the MR sensor 528, thereby outputting 360 pulses per onerevolution. Namely, a signal having a frequency corresponding to therevolution number of the motor is obtained, and this signal is inputtedto the DSP 501 as the MR sensor signal 531 through the amplifier 514.

The DSP 501 measures a pulse interval of the MR sensor signal 531 andseeks the speed (rad/s) of the motor and compares the motor speed with atarget control speed (set target speed which can be altered) andperforms a PI filter (not shown) and gain added calculation (not shown)to derive a PWM pulse width and sends the pulse width to the pre-driver503 as the PWM signal 530 to control the current to be supplied to themotor coil, thereby controlling the motor to rotate at the target speed.

In this way, the DSP 501 effects the switching of the output stageN-chMOS transistor by generating the PWM signal and combines it with theswitching signals, thereby performing servo-control to rotate the motorat the desired number of revolutions. On the other hand, the position ofthe main pole is detected by the hole sensors 525 to 527, and theswitching control is performed by the pre-driver 503 on the basis of thehole sensor signals 415 to 417 to rotate the rotor in the desiredrotational direction. Further, the pre-driver 503 detects the currentflowing through the motor by the electric current detecting resistor521, and, there is provided protecting means for limiting the electriccurrent if the current greater than a predetermined value flows.

FIG. 4 shows an internal construction of the DSP 501 concretely. Thereference numeral 529 denotes six motor start signals outputted to therespective motor units; 530 denotes six PWM signals outputted to therespective motor units; and 531 denotes six motor speed detecting MRsensor signals inputted from the respective motor units.

In FIG. 4, there are shown target speeds 101, 102 for respective motors,in which independent target speeds (rad/s) are set with respect to sixmotors 505 ₁ to 505 ₆; a target speed selecting portion 103 in theservo-control loop; a calculation point 104 for deriving the differencebetween the target speeds and actual speeds; PI filter and PWM selectingportion 105 in the servo-control loop; a PI filter 106 for the motor505, including PI filter integration item constant 107 for the motor505, and a memory portion 108 (of the PI filter for the motor 505 ₁) forstoring a preceding calculation result and a proportion item constant109 of the PI filter for the motor 505 ₁; a PWM pulse width calculationportion 110 for the motor 505 ₁; and a PWM pulse generating portion 111for the motor 505 ₁. The output from the PWM pulse generating portion111 is the PWM pulse signal 530 for the motor 505 ₁.

There are further shown a PI filter 113 for the motor 505 ₆ including PIfilter integration item constant 114 for the motor 505 ₆ and a memoryportion 115 (of the PI filter for the motor 505 ₆) for storing apreceding calculation result and a proportion item constant 116 of thePI filter for the motor 505 ₆; a PWM pulse width calculation portion 117for the motor 505 ₆; and a PWM pulse generating portion 118 for themotor 505 ₆. The output from the PWM pulse generating portion 111 is thePWM pulse signal 530 for the motor 505 ₆.

In this way, the PI filter, the PWM pulse width calculation portion, thePWM pulse generating portion, and the PWM signal are provided for eachof the motors 505 ₁ to 505 ₆.

Further, as the motor speed detecting MR sensor signal 531, 360 pulsesper one revolution of the motor are inputted. A capture 121 serves tocount the pulse obtained by the motor 505 ₁ from edge to edge by apredetermined timer, and a capture 123 serves to count the pulseobtained by the motor 505 ₆ from edge to edge by a predetermined timer.In this way, the pulse signals are given from the respective motors 505₁ to 505 ₆, and the capture is provided for each of the motors. Thereference numeral 124 denotes a capture selecting portion; 125 denotes aspeed calculating portion; and 126 denotes a selector. A CPUcommunication block 128 serves to output motor start signals 529, and aserial communication bus 532 serves to effect communication with acontrol CPU (now shown) of the image forming apparatus.

Next, an operation will be explained.

First of all, the program of the DSP controls the control loop to causethe selector 126 to select a motor to be controlled so that suchcontrols are not interfered with. For example, when six motors arecontrolled with the same control loop of 1 kHz, if all of the motors arecontrolled at the same timing, interference will occur. To avoid this,the phases of the control loops of 1 kHz are deviated from each other.

When the control of the motor 505 ₁ is selected by the selector 126, atarget speed 101 of the motor 505 ₁ is selected, and the selected speedis compared with the speed of the motor 505, at the calculation point104. The speed of the motor 505 ₁ to be compared is sought by inputtingthe pulses (360 pulses per one revolution) generated by the rotation ofthe motor 505 ₁ to the capture 121 through the pulse signal line 120, byselecting it in the capture selecting portion 124, and by calculatingthe speed in the speed calculation portion 125.

A compared result obtained at the calculation point 104 is inputted tothe PWM selecting portion 105, where the PI filter 106 for motor 1 isselected and PI calculation is effected. The PI calculation is effectedby adding a result obtained by multiplying the speed difference (soughtat the calculation point 104) by the proportion item constant 109 to aresult obtained by adding the preceding calculation result (stored inthe memory portion 108) to a result obtained by multiplying the speeddifference by the integration item 107. The proportion constant 109 andthe integration constant 107 (which constitute PI filter constant) arereferred to as the servo constant and are previously set on the basis ofthe specification of the motor, and the load inertia and the torquecondition of the motor.

A calculated result in the PI filter 106 is converted into a PWM pulsewidth in the PWM pulse width calculating portion 110, and the PWM pulseis generated in the PWM pulse generating portion 111. In the PWM pulsegenerating portion, the PWM pulse having the width sought in the PWMpulse calculating portion 111 is overlapped with pre-set PWM carrierfrequency.

For example, when it is defined that the pre-set PWM carrier frequencyis 20 kHz (50 μs) and the PWM pulse width is 8 bits, if the PWM pulsecalculation result is “66”H, the PWM pulse width will be 20 μs (=50μs×“66”H/“FF”H), with the result that the PWM pulse signal 530 of 40%(regarding carrier frequency of 20 kHz) is outputted. The pulse width isrenewed whenever the calculated result is obtained in the PWM pulsecalculating portion 110. Namely, if the PWM calculation is effected witha period of 1 kHz, the PWM pulse width will be changed every 1 kHzperiod.

As mentioned above, similar to the generation of the PWM pulse for themotor 5051, regarding each of the motors 505 ₂ to 505 ₆, a PWM pulse isgenerated on the basis of a corresponding PI filter constant and PWMcarrier frequency. The PI filter constant and PWM carrier frequency arepreviously set in accordance with the specification of the motor and thedriving load condition.

On the other hand, the speed of each of the motors 505 ₁ to 505 ₆selected by the selector 126 is calculated by selecting thecorresponding capture in the capture selecting portion 124 and byreading-in the value of the selected capture and by effectingcalculation in the speed calculating portion 125.

For example, in a case where the capture 121 is 16 bits and clock is 50ns and pulse signal 120 outputted by the motor 505 ₁ has 360 pulses perone revolution, regarding the speed of the motor 505 ₁, when the valueof the capture 121 is “1234”H, the interval between the pulse signal 120becomes 233 μs (=“1234”H×50 ns) and the speed of the motor 505 ₁ becomes74.9 rad/s (=(2π/360)/233 μs).

Next, an operation of the selector 126 will be explained with referenceto FIG. 5. FIG. 5 is a view showing the control of the motors 505 ₁ to505 ₆ in a time-lapse relation. Blocks 801 to 806 indicate controlperiods of the motors 505 ₁ to 505 ₆, a block 807 indicates a controlperiod of the motor 505 ₁, a block 808 indicates the reading of capturein the control of the motor 505 ₁, a block 809 indicates the calculationof speed, a block 810 indicates the setting of target speed, a block 811indicates the calculation of the difference between speeds, a block 812indicates the calculation of PI, a block 813 indicates the calculationof PWM, a block 814 indicates the outputting of PWM, and the referencenumeral 815 indicates a servo-control period of the motor 505 ₁.

Also regarding the motors 505 ₂ to 505 ₆, control similar to the blocks808 to 814 is performed. The servo-control period 815 of the motor 505 ₁is determined by a response property of the motor 505 ₁. Similarly, themotors 505 ₂ to 505 ₆ are controlled with optimum servo-control periodsin consideration of the response properties of the motors. In this case,the servo control periods are controlled by the selector so that theservo-control periods do not interfere with each other.

For example, when the servo-control periods of the motors 505 ₁, to 505₆ are all 1 kHz (1 ms), the control start timing of the motor 505 ₁ isdeviated from the control start timing of the motor 505 ₂ by about 166μs (=1 ms/6). Similarly, deviation between the control start timing ofthe motor 505 ₂ and the control start timing of the motor 505 ₃,deviation between the control start timing of the motor 505 ₃ and thecontrol start timing of the motor 505 ₄, deviation between the controlstart timing of the motor 505 ₄ and the control start timing of themotor 505 ₅, deviation between the control start timing of the motor 505₅ and the control start timing of the motor 505 ₆ are selected to beabout 166 μs.

On the basis of the servo-control period determined for each motorcontrol, the capture of the motor to be controlled is read, the speed iscalculated, the target speed of the motor to be controlled is set, thedifference between the target speed and the actual speed is calculated,a calculated result is subjected to PI calculation with the PI filterconstant for the motor to be controlled, PWM calculation is effected,and the PWM is outputted. Namely, servo-control loops for the respectivemotors are formed so that they do not interfere with each other, and,the target speeds and PI filter constants (servo constants) inherent tothe respective motors are selected, and the respective PWM pulsecontrols are effected.

Next, the motor control operation will be explained.

First of all, for example, when the fixing motor driving command istransmitted from the CPU through the serial communication bus 532, theDSP 501 causes the pre-driver 503 to make the motor start signal 529active and causes the PWM signal 530 to generate a PWM pulse having anON-duty of 80%, thereby driving the motor.

When the motor start signal 529 is received, the pre-driver 503 effectsthe exciting switching control of the N-chMOS transistors 515 to 520 (inthe logic circuit 508) on the basis of the position of the rotordetected by the hole sensors 525 to 527 so that the motor is rotated inthe predetermined rotational direction, and, when the PWM signal 530 isreceived, the pre-driver PWM-switches the N-chMOS transistors 515, 517,519. In this case, the control circuit 509 increases the gate voltagesfor the N-chMOS transistors 515, 517, 519 to Vcc+10V through the chargepump circuit 507.

For example, when the logic circuit 508 ascertains the position of therotor of the motor on the basis of the result amplified by the holesensor amplifiers 511 to 513 and the result sensed by the hole sensors525 to 527 to switch the electric current direction from the U-phase 522to the V-phase 523 thereby to obtain the desired rotational direction,the N-chMOS transistors 515, 518 are turned On and the N-chMOStransistors 516, 517, 519, 520 are turned OFF. As a result, the electriccurrent path extends from Vcc to the electric current detecting resistor521 through the N-chMOS transistor 515, U-phase output 522, W-phaseoutput 523 and N-chMOS transistor 518, thereby generating a magneticforce in the predetermined coil.

In this case, the N-chMOS transistor 515 is PWM controlled by the PWMsignal 530 given by the DSP 501 and passing through the logic circuit508 and control circuit 509. Accordingly, the ON-duty electric currentdefined by the PWM signal 530 flows from the U-phase to the V-phase. Inthis way, the exciting switching control for switching the electriccurrent to the U-phase and V-phase is effected so that the motor isrotated in the predetermined direction, thereby generating torque by therelative electromagnetic action between the main pole magnet (not shown)and the coil.

When the motor is subjected to the exciting switching control to rotatethe rotor in this way, the pre-set MR sensor magnetized pattern isdetected by the MR sensor 528, and 360 pulses per one revolution areoutputted. Namely, the signal having a frequency corresponding to therevolution number of the motor is obtained, and this signal is sent tothe DSP 501 through the amplifier 514 and the MR sensor signal line 531.

The program of the DSP 501 measures the pulse interval between thepulses from the MR sensor signal line 531 and seeks the speed (rad/s) ofthe motor and compares the motor speed with target control speed andperforms a PI filter calculation (not shown) and a gain additioncalculation (not shown) to derive the PWM pulse width and sends thepulse width to the pre-driver through the PWM signal line 530 to controlthe current to be supplied to the motor, thereby controlling the motorto rotate at the target speed.

In this way, the DSP 501 effects the switching of the output stageN-chmos transistor by using the PWM signal 530, thereby performing theservo-control to rotate the motor at the desired number of revolutions.On the other hand, the pre-driver 503 performs the exciting control onthe basis of the position of the main pole detected by the hole sensors525 to 527 to rotate the rotor in the desired rotational direction anddrives the N-chMOS transistor. Further, the pre-driver detects thecurrent flowing through the motor by the electric current detectingresistor 521, and, there is provided protecting means for limiting theelectric current by the current limiter circuit 510 if the currentgreater than a predetermined value flows.

As mentioned above, according to the illustrated embodiment, in orderthat the six motors of the image forming apparatus are subjected tosoftware servo-control by the single DSP so as to control the motors byusing the servo constants pre-set in accordance with various conditionsregarding the control revolution number, the inertia, the torqueconstant, the coil specification and the driving load of each motorwithout interfering the independent servo-control loops of the motorswith each other, there is provided the selector means by which thetimings of servo-control loops of the motors are governed, and thecontrol loop of each motor regarding the target speed, the speeddetection, the PI filter calculation, the PWM calculation and the PWMpulse output is controlled.

As a result, particularly in an image forming apparatus which has aplurality of servo motors and in which a driving load condition ischanged within a wide range, stable servo-control can always berealized, thereby obtaining good image quality.

Further, since the servo-control can be performed efficiently under theconcentrated control of a single DSP, the cost of the image formingapparatus can be reduced.

FIG. 6 is a flow chart of the motor control program of the DSP includingservo constant calculation control, regarding only the motor 505 ₁.

First of all, in a step S601, it is judged whether there is a commandfor determining the servo constant of the motor 505 ₁ from the controlCPU (not shown) of the image forming apparatus. The CPU of the imageforming apparatus sends such command to the DSP in a time period inwhich the motor driving is not required, other than the image formingperiod.

In the step S601, if there is the servo constant setting command, in astep S602, a servo constant setting control flag is set, and, in a stepS603, a timer is set. Then, in a step S604, PWM ON-duty is set to 100%,and, in a step S605, the motor driving signal is made active. Then, in astep S606, it is judged whether the motor speed reaches 63%.

In the step S606, if the motor speed does not reach 63%, the program isjumped and the speed detection and PWM output control are effected. As aresult, the motor starts to rotate with an open loop. On the other hand,in the step S606, if the motor speed reaches 63%, in a step S607, themotor is stopped and the PWM ON duty is made 0%, and, in a step S608,the time is measured on the basis of the previously driven timer.Namely, after the motor is driven with the open loop, a time perioduntil the motor speed reaches 63% is measured.

Then, in a step S609, the inertia is sought. Now, the calculation of theinertia will be described.

The transmission function of the motor can be equivalent to a primarydelay system model, and gain G is represented by the following equation(1):

G=K/(1+sT)  (1)

Where, K=1/Ke, and Ke is the reverse start constant. Further,

T=RJ/(Kt×Ke)  (2)

Where, R is the coil resistance of the motor, J is the load inertia andK is the torque constant of the motor.

Further, the response property of the motor is represented by thefollowing equation (3) on the basis of the above equation (1):

h(t)=K/(1−et/T)  (3)

From the equation (3), when t=T, h(t)≅0.632×K.

Namely, by seeking the time when the speed reaches 63.2% after the motorwas started, from J=(Ke×Kt×t)/R (alteration from the above equation(2)), J can be sought, since R, Kt and Ke of the motor are alreadyknown.

Then, in a step S610, the servo constant is calculated. In thiscalculation, the 0 dB intersecting point of the open loop property ofthe motor is sought by ω=1/T from the above equations (1) and (2) byusing the previously sought inertia J, and, an inflection point of thePI filter is set with respect to the intersecting point, and the PIfilter constant (proportion item constant and integration item constantshown in FIG. 4) is sought.

Then, in a step S611, the servo constant setting flag is cleared, andthe servo constant setting sequence is finished. In a step S612, it isjudged whether the motor has already been driven. If not driven, in astep S613, initial setting of resistors, timers and ports is effected,and, in a step S614, the motor is driven. On the other hand, if themotor has already been driven, the program is jumped.

Then, in a step S615, it is judged whether there is CAPI interruption.If there is the interruption, in a step S616, the motor speed iscalculated. This interruption is generated whenever the rising edge ofthe pulse is reached from the MR sensor. On the other hand, if there isno interruption, the program is bypassed.

Then, in a step S617, it is judged whether there is the servo constantsetting control flag. If there is no servo constant setting controlflag, in a step S618, it is judged whether there is servo-control loopinterruption. If there is control interruption, in a step S619, thedifference between the target speed and the actual speed is calculated,and, in a step S620, PI filter calculation is effected by using thepreviously sought constant, and, in a step S621, the PWM width is set.

On the other hand, in the step S617, if under the servo constant settingcontrol, in a step S618, the program bypasses the steps S619 to S621(PWM width calculating sequence). Further, in the step S618, if there isno servo-control interruption, the PWM width calculating sequence isbypassed.

Then, in a step S622, it is judged whether there is a PWM interruption.If there is an interruption, in a step S623, the pulses are outputted tothe port; whereas, if there is no interruption. the pulses are notoutputted. The PWM interruption is generated at carrier frequencypre-set. For example, when the carrier frequency is 20 kHz, interruptionof 20 kHz is generated.

Whenever this interruption is generated, if the PWM pulse having thewidth sought by calculation is outputted, the PWM pulse having carrierof 20 kHz can be formed.

In this way, according to the illustrated embodiment, there is provideda leaning sequence in which the motor servo constant setting period isgiven by the control CPU of the image forming apparatus in the timeperiod other than the image forming period, and, in this period, the DSPcalculates the load inertia of the motor, and the servo constant issought on the basis of the inertia. With this arrangement, for example,even in a system in which the load inertia is greatly changed inaccordance with the difference in toner capacity of the toner cartridgeor the difference in the kind of the cartridge, the proper servoconstant can be used, with the result that the control is stabilized andgood image quality can be obtained.

FIGS. 7A and 7B are views showing a DC brushless motor of theinner-rotor type used in the present invention and a brushless motor ofthe outer-rotor type. In FIG. 7A, a DC brushless motor of theouter-rotor type comprises a rotor 701, stators 702 and windings orcoils 703. On the other hand, in FIG. 7B, a DC brushless motor of theinner-rotor type comprises a rotor 704, stators 705 and windings orcoils 706. As can be seen from the drawings, the motor of theinner-rotor type has smaller rotor which leads to a small inertia.

Namely, since the inertia is the small, the mechanical response of themotor becomes fast accordingly, with the result that the frequency ofthe servo-control loop in the servo-control block diagram of FIG. 4 canbe hastened. That is to say, in a system having relatively great loadfluctuation frequency, by hastening the frequency of the servo-controlloop, the fluctuation suppressing effect due to servo can be enhanced.

In this way, in the illustrated embodiment, by using the above-mentionedmotor servo-control and by using the DC brushless motor of the innerrotor type having a small inertia, the present invention is effective ina system in which rotational fluctuation of the motor due to loadfluctuation is generated at a relatively high frequency.

FIG. 8 shows a first alteration of the internal circuitry of the motorunit shown in FIG. 3. In this alteration, the servo constant isdetermined in accordance with the kind of the motor. The same (elementsas those in the embodiment shown in FIG. 3 are designated by the samereference numerals and an explanation thereof will be omitted.

In FIG. 8, the reference numerals 533, 534 indicate discriminationsignals of the motor unit. In this alteration, discrimination signallines (discrimination signals 533, 534 for the motor) are provided inassociation with the servo-control apparatus. The DSP 501 determines theservo constant on the basis of the motor discrimination signals 533,534.

For example, when it is assumed that the outer rotor motor is designatedif the motor discrimination signals 533, 534 are “0”, “1”, respectively,and the inner rotor motor is designated if the motor discriminationsignals 533, 534 are “1”, “1”, respectively, the DSP 501 selects thecorresponding servo constant from the servo constant table previouslystored for the respective motors and effects servo-control. Bydiscriminating the motor type on the basis of the motor discriminationsignals 533, 534 and by selecting and using the optimum servo constantfor the motor, stable motor servo-control can be realized.

Next, the motor servo-control effected by the DSP 501 will be explained.

FIG. 9 is a flow chart showing a servo-control routine of the DSP 501shown in FIG. 8.

First of all, in a step 401, it is judged whether the servo constant isset. If No, in a step 402, the motor type is discriminated. Thisdiscrimination is effected by using the motor discrimination signals533, 534 shown in FIG. 8.

Then, in a step 403, the servo constant corresponding to the result ofthe discrimination signals is derived from the lookup table. The lookuptable is previously stored in a memory (not shown) of the DSP. Further,the servo constant indicates constants of the proportion item and theintegration item of the PI filter and a constant of gain.

Then in a step 404, the derived servo constant is set in a calculationformula.

On the other hand, in the step 404, after the servo constant was setonce, when the servo-control routine is carried out again, in the step401, it is judged that the servo constant has already been set, and theroutine jumps to a step 405.

Then, in steps 405 to 407, it is judged whether the motor is started orstopped.

In a control task (not shown), when a motor start flag or a motor stopflag is set and the servo-control routine is carried out, in the step405, the flag is checked. If it is judged that the motor should bestarted in the step 405, the motor drive signal 529 is made active, and,in the step 407, the predetermined PWM value is given, therebyaccelerating the motor. On the other hand, if it is judged that themotor should be stopped in the step 405, in the step 406, the motordrive signal 529 is made disable to make the PWM signal zero, therebystopping the motor.

Then, in a step 408, it is judged whether there is interruption ofcapture. The capture circuit (not shown) is designed so that, wheneverthe rising edge of the pulse of the MR sensor signal 331 shown in FIG. 8is reached, such capture interruption is generated.

In the step 408, if there is the interruption of capture, in a step 409,interval between the interruptions is measured to derive the number ofrevolutions of the motor. For example, when it is assumed that 300 MRsensor pulses are generated per one revolution and the pulse interval ist (s), the rotational speed of the motor becomes (2π/300÷t) rad/s. Onthe other hand, in the step 408, if there is no capture interruption,the motor speed is not calculated.

Then, in a step 410, it is judged whether there is control interruption.It is designed so that, when the servo-control loop effects the controlwith 1 kHz, interruption of 1 kHz is generated. If the interruption isgenerated, in a step 411, the pre-set target speed with the actual speeddetected by the capture, and a result is PI-calculated in a step 412.The proportion item constant, integration item constant and gainconstant set in the step 404 are calculated, and a result isPWM-calculated in a step 413, thereby deriving the PWM width. As aresult, the desired PWM widths are outputted at an interval of 1 kHz.Namely, the servo-control loop having a control frequency of 1 kHz canbe realized.

Then, in a step 414, it is judged whether there is PWM interruption.

This interruption is generated every 20 kHz by a pre-designed PWMcircuit (not shown).

In the step 414, if the PWM interruption is detected, in a step 415, thepulses having PWM width previously sought in the step 413 are outputted.On the other hand, if the PWM interruption is not detected, the PWMoutput is not effected. In this way, the PWM pulse having carrierfrequency of 20 kHz can be outputted.

As mentioned above, in the first alteration, the motor type isdiscriminated by the type discrimination signals provided in each motorunit, and, on the basis of this, the servo constant corresponding to themotor type is derived from the table, and the servo-control is performedby using this servo constant.

Next, a circuit operation of this motor servo-control circuit will beexplained. First of all, when the motor drive command is transmittedfrom the CPU through the serial communication line 532, the pre-driver503 ascertains the position of the rotor detected by the hole sensors525 to 527 and determines the switching timing to obtain the desiredrotation and effect control so as to obtain the desired rotationaldirection and to cause the desired electric current to flow into themotor coil.

Namely, the switching control of the N-chMOS transistors 515 to 520 iseffected to obtain the desired rotational direction, and the N-chMOStransistors 515, 517, 519 are PWM-switched to cause the desired currentto flow into the coil. In this case, the gate voltages for the N-chMOStransistors 515, 517, 519 are increased to Vcc+10V by the charge pumpcircuit 507.

For example, when the pre-driver 503 ascertains the position of therotor of the motor on the basis of the hole sensor signals amplified bythe hole sensor amplifiers 511 to 513 and the hole sensors 525 to 527and switches the electric current direction from the U-phase 522 to theW-phase 523 to obtain the desired rotational direction, the pre-driver503 turns ON the N-chMOS transistors 515, 518 and turns OFF the N-chMOStransistors 516, 517, 519, 520. As a result, the electric current pathextends from Vcc to the electric 25 current detecting resistor 521through the transistor 515, U-phase output 522, V-phase output 523 andtransistor 518, thereby generating a magnetic force in the predeterminedcoil. In this case, the PWM signal 530 given by the DSP 501 is combinedwith the switching signals, and the N-chMOS transistors 515 isPWM-controlled by the pre-driver 503.

Accordingly, the ON-duty electric current defined by the PWM signalflows from the U-phase to the V-phase. In this way, the excitingswitching control for switching the electric current to the U-phase,V-phase and W-phase is effected so that the motor is rotated in thepredetermined direction, thereby generating torque by relativeelectromagnetic action between the main pole magnet (not shown) and thecoil.

When the motor is subjected to the exciting switching control to rotatethe rotor in this way, the pre-set MR sensor magnetized pattern isdetected by the MR sensor 528, and 360 pulses per one revolution areoutputted. Namely, the signal having frequency corresponding to therevolution number of the motor is obtained, and this signal is sent tothe DSP 501 through the amplifier 514 and the MR sensor signal 531.

The DSP 501 measures the pulse interval between the pulses from the MRsensor signal line 531 and seeks the speed (rad/s) of the motor andcompares the motor speed with the target control speed (set target speedwhich can be altered) and performs PI filter calculation (not shown) andgain addition calculation (not shown) to derive the PWM pulse width andsends the pulse width to the pre-driver 503 as the PWm signal 530 tocontrol the current to be supplied to the motor, thereby controlling themotor to rotate at the target speed.

In this way, the DSP 501 generates the PWM signal and effects theswitching of the output stage N-chMOS transistor by combining the PWMsignal with the switching signals, thereby performing the servo-controlto rotate the motor at the desired number of revolutions. On the otherhand, the position of the main pole is detected by the hole sensors 525to 527, and the pre-driver 503 performs the switching control by usingthe hole sensor signals to rotate the rotor in the desired rotationaldirection. Further, the pre-driver 503 detects the current flowingthrough the motor by the electric current detecting resistor 521, and,there is provided protecting means for limiting the electric current bythe current limiter circuit 510 if the current greater than apredetermined value flows.

FIG. 10 shows a second alteration of the internal circuitry of the motorunit shown in FIG. 3. The same elements as those in the embodiment shownin FIG. 3 are designated by the same reference numerals and anexplanation thereof will be omitted.

The second alteration shown in FIG. 10 differs from the first alterationshown in FIG. 8 in the point that, in place of the motor discriminationsignals 533, 534, a memory 535 is provided in a motor unit 502, and theDSP 501 and the motor unit 502 effect communication through serialcommunication.

An operation will be explained with reference to FIG. 11.

FIG. 11 is a flow chart of the servo-control of the DSP 501 shown inFIG. 10.

First of all, in a step 601, it is judged whether the servo constant isset. If No, in a step 602, the serial communication to the motor unit iseffected to read-in the contents of the memory of the motor unit,thereby recognizing control information of the motor unit.

Then, in a step 603, the information recognized in the previous step,i.e., servo constant is set.

On the other hand, in the step 603, after the servo constant was setonce, when the servo-control routine is carried out again, in the step601, it is judged that the servo constant has already been set, and theroutine jumps to a step 604.

Then, in steps 604 to 606, it is judged whether the motor is started orstopped.

In a control takes (not shown), when a motor start flag or a motor stepflag is set and the servo-control routine is carried out, in the step604, the flag is checked. If it is judged that the motor should bestarted in the step 604, in a step 605, the motor drive command is sentto the motor unit by serial communication, and the predetermined PWMvalue is given, thereby accelerating the motor.

On the other hand, if it is judged that the motor should be stopped inthe step 604, in the step 606, the motor stop command is sent to themotor unit by serial communication, and the PWM value is made zero,thereby stopping the motor.

Since steps 607 to 614 are the same as the sets 408 to 415 in FIG. 4, anexplanation thereof will be omitted.

In this way, in the second alteration, the communication between the DSPand the motor unit is effected by serial communication, and the memorymeans is provided in the motor unit, and the motor control parametersare previously stored in the memory means.

The DSP reads-in the servo constant of the motor through the serialcommunication, and the servo-control is effected on the basis of theservo constant.

Accordingly, the lookup table memory in the motor unit of the firstalteration can be omitted, and many control parameter information can bestored in the motor unit, thereby further improving the servo-controlaccuracy.

In the present invention, while an example that the six motors are usedwas explained, the number of motors is not limited to plural motors,but, the present invention can be applied to a single motor.

As mentioned above, according to the present invention, the motorservo-control apparatus, which can cope with a change in speed of themotor quickly and stably, can be obtained.

In the motor servo-control apparatus according to the present invention,since the DSP effecting quick product/addition calculation by obtainingthe PWM signal by inputting the rotational speed signal from the MRsensor to the DSP, the apparatus is suitable for servo-control, and,since control conditions can be programmed in accordance with loadconditions (torque, inertia, gain and the like), the control hasflexibility.

By combining the PWM signal from the DSP with the directly inputtedswitching signal in the pre-driver, the number of signal lines (numberof pins) can be reduced. Further, by controlling the plurality ofmotors, the number of signal lines can be reduced.

By controlling the servo-control of the plural motors collectively bythe single DSP, the total cost of the system can be reduced, and thesystem control of the plural motors can easily be performed.

Further, by using the motor servo-control apparatus having theabove-mentioned construction in the image forming apparatus, in an imageforming apparatus including a plurality of servo motors, by effectingthe servo-control by using means for determining the servo constant ofthe motors in accordance with the load conditions for the driving of theservo motors and means for measuring the load inertia in the time periodother than the image forming period and for calculating the servoconstants on the basis of measured results, even in a system in whichload inertia and torque are greatly differentiated, since the optimumservo constants are always set, the stable motor servo-control can beachieved, thereby obtaining the good image quality.

Further, by providing means for effecting control without interferencebetween the plural servo-control loops, the plurality of motors can beservo-controlled independently by the single processor, thereby reducingthe system cost.

Further, by using the DC brushless motor of inner rotor type havingsmall inertia as the driving motor to hasten the servo-control loop,even in the load in which period of rotation fluctuation due to loadfluctuation is relatively high, the stable servo-control can beeffected.

According to the present invention, means for discriminating the servomotor type are provided, and the servo constant is determined by thismeans, and the motor is servo-controlled on the basis of the servoconstant. Alternatively, the servo motor is provided with the memorymeans in which the servo constant is stored, and, by effecting theservo-control on the basis of read-out servo constant, even in anapparatus in which a plurality kinds of motors are used, the respectivemotors can always be servo-controlled with optimum servo constants.

Particularly, as is in an image forming apparatus, in a system in whichmotors manufactured by plural manufacturers are used in the same drivingarea, by discriminating the motor type or by directly getting the servoconstant information optimum to the motor and by effecting theservo-control on the basis of the motor type or servo constantinformation, not only stability of the motor servo-control is enhancedbut also the motors having different properties and manufactured byplural manufactures can be used similarly without changing the controlprogram and the arrangement of the image forming apparatus, therebyimproving productivity and motor supplying stability.

What is claimed is:
 1. A servo-control apparatus for a motor,comprising: rotational speed signal generating means for generating arotational speed signal corresponding to a rotational speed of a motor;digital control means for generating a pulse width modulated signal fordetermining an exciting electric current to be supplied to a coil ofsaid motor in accordance with the rotational speed signal from saidrotational speed signal generating means; position detecting means fordetecting a rotational position of said motor and for generating aposition detection signal corresponding to a detected position; apre-driver for forming a switching signal for switching the excitingelectric current to be supplied to said coil of said motor in accordancewith the position detection signal from said position detecting meansand for combining the switching signal with the PWM signal from saiddigital control means to generate an electric current control signal;and a driver for driving said motor on the basis of the electric currentcontrol signal from said pre-driver.
 2. A servo-control apparatusaccording to claim 1, wherein said digital control means have thereintarget speed setting means for setting a target speed which can bealtered and generate the pulse width modulated signal in accordance withthe target speed from said target speed setting means and the rotationalspeed signal from said rotational speed signal generating means.
 3. Aservo-control apparatus according to claim 1, wherein said pre-driverhas a logic circuit for combining the switching signal with the pulsewidth modulated signal, and a control circuit for boosting an outputsignal from said logic circuit to output it as the electric currentcontrol signal.
 4. A servo-control apparatus according to claim 1,wherein said digital control means are a digital signal processor.
 5. Aservo-control apparatus for servo-controlling a plurality of motors,comprising: a plurality of rotational speed signal generating means forgenerating rotational speed signals corresponding to rotational speedsof said plurality of motors, respectively; digital control means forgenerating pulse width modulated signals for determining excitingelectric currents to be supplied to coils of said plurality of motors inaccordance with the rotational speed signals from said plurality ofrotational speed signal generating means, respectively; a plurality ofposition detecting means for detecting rotor positions of said pluralityof motors, respectively; a plurality of pre-drivers for formingswitching signals for switching the exciting electric currents to besupplied to said coils of said plurality of motors in accordance withrotor position detection results from said plurality of rotor positiondetecting means and for combining the switching signals with the pulsewidth modulated signals from said digital control means to generateelectric current control signals, respectively; and a plurality ofdrivers for driving said plurality of motors on the basis of theelectric current control signals from said pre-drivers.
 6. Aservo-control apparatus according to claim 5, wherein the motorservo-control apparatus is used in an image forming apparatus.
 7. Aservo-control apparatus for a motor, comprising: rotational speed signalgenerating means for generating a rotational speed signal correspondingto a rotational speed of a motor; digital control means for generating apulse width modulated signal for determining an exciting electriccurrent to be supplied to a coil of said motor in accordance with therotational speed signal from said rotational speed signal generatingmeans; position detecting means for detecting a rotational position ofsaid motor and for generating a position detection signal correspondingto a detected position; switching signal generating means for generatinga switching signal for switching the exciting electric current to besupplied to said coil of said motor in accordance with the positiondetection signal from said position detecting means; and a driver fordriving said motor on the basis of the switching signal from saidswitching signal generating means and the pulse width modulated signalfrom said digital control means.
 8. A servo-control apparatus for amotor, comprising: rotational speed signal generating means forgenerating rotational speed signals corresponding to rotational speedsof a plurality of motors; and digital control means for determiningexciting electric currents to be supplied to coils of said plurality ofmotors in accordance with the rotational speed signals from saidrotational speed signal generating means; and wherein said digitalcontrol means comprise target speed setting means for setting targetspeeds, rotational speed calculating means for obtaining the rotationalspeeds from said rotational speed signal generating means, and servocalculation means for adding servo constants to differences between thetarget speeds from said target speed setting means and the rotationalspeeds from said rotational speed calculating means, servo-control meansfor determining the electric currents to be supplied to said coils ofsaid motors on the basis of results of said servo calculation means andproviding the electric currents in association with said respectivemotors, and timing control means for controlling control timings of saidservo-control means for said respective motors.
 9. A servo-controlapparatus according to claim 8, wherein said digital control meanscomprise servo constant setting judging means for judging whether aservo constant is set, and servo constant setting means for setting theservo constant when it is judged that the servo constant should be setby said servo constant setting judging means.
 10. A servo-controlapparatus according to claim 8, wherein said timing control meanscomprise target speed selecting means for selecting target speeds forsaid motors, means for selecting the servo constants and said servocalculation means for said motors, rotational speed calculating meansfor obtaining the rotational speeds from said rotational speed signalgenerating means, and means for selecting speed information from therotational speed signals for said motors, and further wherein theselection is effected in a time-lapse fashion for said motors.
 11. Aservo-control apparatus according to claim 9, wherein said servoconstant selecting means measure a time period until said motor reachesa predetermined speed and calculate the servo constant from a measuredresult.
 12. A servo-control apparatus according to claim 8, wherein eachof said motors is a motor of an inner rotor type having a stator coilfor generating a magnetic field in an excited condition, and a rotormagnet for obtaining a rotational force under the relativeelectromagnetic action with an electric current magnetic field withinsaid stator coil.
 13. A servo-control apparatus for a motor, comprising:recognizing means for recognizing the kind of motor with which saidservo-control apparatus is used; rotational speed signal generatingmeans for generating a rotational speed signal corresponding to arotational speed of said motor; and digital control means for generatinga pulse width modulated signal for determining an exciting electriccurrent to be supplied to a coil of said motor in accordance with therotational speed signal from said rotational speed signal generatingmeans; and wherein said digital control means comprise target speedsetting means for setting a target speed, rotational speed calculatingmeans for obtaining the rotational speed from said rotational speedsignal generating means, and servo calculation means for adding a servoconstant in accordance with a difference between the target speed fromsaid target speed setting means and the rotational speed from saidrotational speed calculating means and a recognition result from saidrecognizing means, thereby generating the pulse width modulated signalto be supplied to said coil of said motor in accordance with acalculation result of said servo calculation means.
 14. A servo-controlapparatus according to claim 13, wherein said recognizing meansrecognize the torque constant and inertia of said servo motor.
 15. Aservo-control apparatus according to claim 13, wherein said recognizingmeans have recognizing signal generating means corresponding to the kindof the motor and determine the servo constant of said servo calculationmeans of said digital control means in accordance with a recognizingsignal from said recognizing signal generating means.
 16. Aservo-control apparatus according to claim 13, wherein said recognizingmeans have a memory storing a recognizing signal corresponding to thekind of the motor and determine the servo constant of said servocalculation means of said digital control means in accordance with therecognizing signal from said memory.
 17. A servo-control apparatusaccording to claim 13, wherein there are provided a plurality of saidmotors and a plurality of said rotational speed signal generating means,and said digital control means generate the pulse width modulatedsignals for determining the exciting electric currents to be supplied tosaid coils of said plurality of motors, respectively and servo-controlsaid plurality of motors collectively.
 18. A servo-control apparatus fora motor, comprising: recognizing means for recognizing the kind of motorwith which said servo-control apparatus is used; rotational speed signalgenerating means for generating a rotational speed signal correspondingto a rotational speed of said motor; and digital control means forgenerating a pulse width modulated signal for determining an excitingelectric current to be supplied to a coil of said motor in accordancewith the rotational speed signal from said rotational speed signalgenerating means, said digital control means comprising target speedsetting means for setting a target speed, rotational speed calculatingmeans for obtaining the rotational speed from said rotational speedsignal generating means, and servo calculation means for adding a servoconstant in accordance with a difference between the target speed fromsaid target speed setting means and the rotational speed from saidrotational speed calculating means and a recognition result from saidrecognizing means, thereby generating the pulse width modulated signalto be supplied to said coil of said motor in accordance with acalculation result of said servo calculation means; position detectingmeans for detecting a rotational position of said motor and forgenerating a position detection signal corresponding to a detectedposition; a pre-driver for forming a switching signal for switching theexciting electric current to be supplied to said coil of said motor inaccordance with the position detection signal from said positiondetecting means and or overlapping the pulse width modulated signal fromsaid digital control means with the switching signal; and driver fordriving said motor on the basis of the switching signal overlapped bythe pulse width modulated signal from said pre-driver.
 19. Aservo-control apparatus for switching exciting electric currents to besupplied to coils of a motor in accordance with a rotor positiondetection result of said motor and for controlling the exciting electriccurrents to be supplied to said coils of said motor on the basis of arotational speed signal corresponding to a rotational speed of saidmotor, comprising: recognizing means for recognizing the kind of saidmotor with which said servo-control apparatus is used; digital controlmeans for determining a servo constant in accordance with a recognitionresult of said recognizing means and for generating a pulse widthmodulated signal for determining the exciting electric current to besupplied to said coil of said motor in accordance with the servoconstant and the rotational speed signal; switching signal generatingmeans for generating switching signals for switching the excitingelectric currents to be supplied to said coils of said motor inaccordance with the rotor position detection result; and a driver fordriving said motor on the basis of the switching signal from saidswitching signal generating means and the pulse width modulated signalfrom said digital control means.
 20. A servo-control apparatus for amotor, comprising: rotational speed detecting means for detecting arotational speed of a motor; digital control means for generating apulse width modulated signal for controlling the rotational speed ofsaid motor in accordance with the rotational speed detected by saidrotational speed detecting means; position detecting means for detectinga rotational position of said motor; and electric current generatingmeans for generating an electric current control signal for driving saidmotor, in accordance with said pulse width modulation signal from saiddigital control means and the rotational position detected by saidposition detecting means.
 21. A servo-control apparatus for a motor,comprising: receiving means for receiving from a digital signalprocessor, a pulse width modulated signal for controlling the rotationalspeed of said motor; position detecting means for detecting a rotationalposition of said motor; and electric current generating means forgenerating an electric current control signal for driving said motor, inaccordance with said pulse width modulation signal received from saiddigital signal processor and the rotational position detected by saidposition detecting means.